Apparatus and method for determining analyte content in a fluid

ABSTRACT

An apparatus and method to determine analytes in a fluid. One aspect of the present invention is for the determination of the oil content of water using UV, near-IR, IR or Raman spectroscopy or radiometry. In certain embodiments, a solid membrane material absorbs analytes from fluid brought into contact with it. The membrane is subsequently placed in a FTIR spectrometer, which spectrometer is enabled to determine the concentration of analytes in fluid by calibration. Certain embodiments can determine the type of hydrocarbon present, and thus can differentiate Total Petroleum Hydrocarbons (TPH) from Total Oil and Grease (TOG), without any separate sample preparation.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 12/324,688 entitled “APPARATUS AND METHOD FORDETERMINING ANALYTE CONTENT IN A FLUID”, filed on Nov. 26, 2008, whichclaims the priority benefit of U.S. provisional application Ser. No.61/020,063 filed Jan. 9, 2008 and U.S. provisional application Ser. No.61/081,620 filed Jul. 17, 2008. The entire contents of all of thepriority applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to devices and techniques used todetermine the analyte content in a fluid. More particularly, the presentinvention relates to systems and methods for capturing analytes on atest bed for subsequent analysis in a test device. More specifically,the present invention relates to devices and methods for determininghydrocarbon content in water.

2. Description of the Prior Art

There is a need for a new fast and economical hydrocarbon in watermeasurement technique that directly measures the oil content of waterand does not require the use of any solvents. Infrared absorptionmeasurements have been the preferred basis of measurement for overtwenty years. However, these measurements require first performing aliquid-liquid extraction to remove the hydrocarbon from the water. Thepreferred solvents for performing the extraction, such as Freon, S-316,and perchloroethylene have been banned or are being phased out due toenvironmental, health, and safety concerns. The sensing and detectionindustry response to this challenge has been to introduce new methodsand instruments not based on IR absorption.

As used herein, “hydrocarbon” means all molecules containing hydrogenand carbon; examples include aliphatic and aromatic molecules as well ascarboxyl groups in carboxylic acids or ester groups. As used herein,“oil” means a mixture of aliphatic hydrocarbons with generally betweenseven and 40 carbons in the chain, aromatic species, and otherhydrocarbons. It includes crude oil, refined oil, heating oil, and anyother form of carbon-based oil.

The current method for measuring hydrocarbons in water approved by theOslo-Paris Convention (OSPAR) for use in Europe and Scandinavia is GasChromatography-Flame Ionization Detection (GC-FID) (OSPAR CommissionReference Number 2005-15). The method requires the use of solvent(pentane is recommended) to perform a liquid-liquid extraction forsample preparation. This method has the advantage of directly measuringthe oil content and differentiating TPH from BTEX and Grease. However,GC-FID is extremely time consuming and labor intensive, requiring up toan estimated 6 hrs per measurement and many more for periodicrecalibrations. Also, the differentiation of TPH from Grease content isnot inherent in the measurement technique but instead requires separatesample preparation by an experienced operator.

As used herein, “TPH” means Total Petroleum Hydrocarbons, generallyincluding non-volatile aliphatic molecules of varying chemical structurewith up to 40 carbons. As used herein, “BTEX” stands for all aromaticorganic molecules, including Benzene, Toluene, Ethylbenzene, and ortho-,meta- and para-Xylene. As used herein, “Grease” refers to long chainhydrocarbon molecules containing carboxylic acid and/or ester functionalgroup or groups.

The current US standard method for measuring hydrocarbons in waterapproved by the Environmental Protection Agency (“EPA”) (EPA 1664) toreplace the previous IR-based methods (EPA 418.1 and 413.2) is alsobased on liquid-liquid extraction. Simply, after extracting the oil fromthe water into a solvent, generally hexane, the hexane is evaporated andtotal mass of material remaining is measured and reported as the TPH orTOG (as used herein, “TOG” means Total Oil and Grease; that is, thetotal of TPH and Grease and excluding BTEX). The EPA 1664 method alsointroduced new terminology specific to the method. Instead of TOG, EPA1664 refers to Hexane Extractable Material, or HEM. Instead of TPH, EPA1664 refers to Silica Gel Treated Hexane Extractable Material, orSGT-HEM. Differentiating TOG (or HEM) from TPH (or SGT-HEM) requiresseparate sample preparation by the operator. This method is also laborintensive and the measurement takes a long time. It must be ensured thatthere is no water present and all the hexane is evaporated, as thepresence of either will result in over-reporting the TPHI/TOG content ofthe sample. This means one measurement can take up to 48 hrs. In arevision to EPA 1664, the EPA has promulgated EPA 1664A, a techniquethat allows solid phase extraction (SPE) of the HEM from water using SPEdiscs or cartridges, followed by the elution of the HEM from the SPEmaterial with hexane. As in EPA 1664, the hexane is then evaporated fromthe sample and the remaining material is weighed to determine HEM.SGT-HEM is determined by re-dissolving the HEM in hexane to perform thesilica gel treatment. While EPA 1664A reduces the amount of solventrequired and the time to perform the test, it cannot be used on certainsamples due to clogging issues and does still require significantsolvent use (about 200 ml of hexane per test) and time (about 1.5 hrsfor most samples).

Other competing measurement techniques are based on the ultravioletfluorescence, ultraviolet absorbance, or simultaneous spectralultraviolet fluorescence/absorbance of the BTEX components of the oilcontent. They have the advantage of being capable of measuring very lowamounts (as low as 50 ppb has been claimed) of BTEX in water andmeasuring the sample in water with no liquid-liquid extraction samplepreparation step. However, since this method is based on measuring justthe aromatic (BTEX) component of the sample, the presence of TPH and/orGrease must be determined by calibration of the expected oil stream bysome method that can measure all three components. This issue is asignificant drawback when performing measurements for regulatorycompliance, which generally require the measurement of all the pollutingcomponents of the aqueous sample of interest, and when unknown oilcontaminant streams are encountered.

Light scattering/turbidity is the other major non-IR based technique inuse for oil in water analysis. This technique relies on the fact thatoil is very slightly soluble in water (generally below 1 ppm) and so itis actually a two-phase system, i.e., oil is present as droplets inwater. These droplets scatter light of certain wavelength depending onthe droplet size and the intensity of the scattering at a certainwavelength depends on both the number of droplets and droplet size.Therefore, the number and size of oil droplets can be measured byexamining the light scattering profile of the flowing two phase fluidsystem. However, problems are encountered with gas bubbles and solidparticles also scattering light, thus leading to overestimating the oilcontent of the sample. The walls of such a device must be transparent tothe wavelength range of interest at the point the measurement isperformed. However, oil and other potential contaminates in the samplewill tend to rapidly foul all surfaces, necessitating thorough cleaningafter relatively short periods of operation.

Other methods, such as those based on ultrasonic acoustic pulse echo,are unproven and highly complex and thus unlikely to find wideacceptance.

German Patent No. DE2754293 describes a particular extraction solventfor use in automated systems available from HORIBA, Ltd, of 2Miyanohigashi, Kisshoin, Minami-ku Kyoto 601-8510 Japan. These systemswere designed for use to comply with EPA 418.1, and so are essentiallymade obsolete by the banning or phasing out of most extraction solvents.While these systems use the infrared radiation absorbing property ofhydrocarbons as the basis for sensing oil in water, they require the useof solvent for liquid-liquid extraction.

The standard practice worldwide generally required the use ofchlorofluorocarbon solvents, which are harmful to the ozone layer andhave generally been banned worldwide, or other extraction solvents, suchas perchloroethylene, which are hazardous to the health and safety ofthe operator and are also being phased out worldwide. Therefore, thesolvent-based systems are generally obsolete in practice. Some othersystems provide for the capture and regeneration of the extractionsolvent for reuse, but this is generally considered insufficientenvironmentally.

U.S. Pat. No. 5,109,442 describes a hydrophobic material such as Teflon®(available from the DuPont Company of Delaware) that is used solely as awaterproofing component and not as a hydrocarbon-absorbing material asin the present invention, but the use of that system containing Teflon®material for oil in water measurement is not described. In general, theabsorptive film consists of a metal having a refractive index thatchanges when in contact with various analytes. This metal film is coatedon an optical fiber through which light of some unknown frequency ispassed, but which cannot be infrared radiation due to the fiber opticmaterial. The change in refractive index of the cladding results in achange in the light signal exiting the optical fiber which is correlatedto the concentration of analyte in the gas or liquid being measured.Therefore, this technique does not directly measure the oil content, butinstead measures a change in a secondary material property (refractiveindex) of the cladding. Also, it is explicitly stated that platinumcladding responds strongly to the BTEX components, so in effect thesensing methodology is twice removed from directly measuring the oilcontent. That is, the device is measuring a secondary material propertyresponse to only a small portion of the total hydrocarbon content in thewater. The technique therefore relies on calibrations of the totalhydrocarbon content relative to the content of BTEX compounds which isoften unknown and or changing with time.

In “Determination of oil and grease by sold phase extraction andinfrared spectroscopy”, Analytica Chimica Acta 395 (1999) 77-84), Ferrerand Romero describe a method which requires a vacuum filtrationapparatus to perform the oil separation from water. A vacuum filtrationmethod fails to supply sufficient pressures to ensure fluid flow in atimely manner (i.e. <10 minutes) through a membrane due to filterclogging. This limitation is significant since real-world samplestypically contain high levels of metals/metal oxide particles, organicmaterials, and other particulates which clog and consequently inhibitfluid flow though the membrane unless sufficiently high differentialpressures across the membrane are applied.

The Romero method further requires the membrane to be physically handledand extracted from the vacuum filtration apparatus, then re-attached toa different membrane holder via magnetic supports for post-collection IRanalysis. Among other things, this can lead to undesirable collectorcontamination and delays in the analysis process. These and otherlimitations of the Romero method as described in the noted referenceresult in a system that is not adequate for commercialization.

Ferrer and Romero further describe another system for the determinationof hydrocarbons in water in “Fourier Transform Infrared Spectroscopy andSolid Phase Extraction Applied to the Determination of Oil and Grease inWater Matrices,” Microchemica Acta 140, 35-39(2002), which consists of avaporizing hydrocarbons out of the water sample and onto a PTFE discsuspended above the water surface. The method is recommended by theauthors mainly for use on diesel and petrol-containing samples, as theprocessing conditions (heat and time, up to 14 hours in some cases) andcalibration to be used vary considerably with the type of hydrocarbonpresent in the water sample. The described method thus is not widelyapplicable or commercially viable.

While the description of the prior art has been directed to thedetermination of hydrocarbon content in water, it is to be noted moregenerally that Based on the foregoing, there is a need for acommercially suitable apparatus and related method to detect analytes influids with reasonable accuracy. In general, it is desirable to have ananalyte determination apparatus and method that effectively retainsaccurate and reliable samples of the analyte for evaluation using knownevaluation tools including, but not limited to, IR spectroscopy.

SUMMARY OF THE INVENTION

The present invention is directed toward a commercially suitableapparatus and related method to detect analytes in fluids. Morespecifically, the present invention is directed toward an apparatus anda method for analyte determination that effectively retains accurate andreliable samples of the analyte for evaluation using known evaluationtools.

The apparatus for performing the method includes a fixture with ananalyte-retaining membrane selected for minimal or no interaction withthe analyte or analytes of interest. In certain embodiments, themembrane material is configured as part of the test fixture in a mannerthat ensures it will absorb or otherwise capture the analyte of interestfrom fluid brought into contact with it. The membrane either alone or ina portion or all of the test fixture, is subsequently placed in aspectrometer, radiometer or other detection tool and processed. Thecontent and concentration of analytes retained on the membrane are thencalculated using analysis software, for example.

The apparatus of the present invention includes a sampling device, anoptional sample pre-treatment subsystem, a sample preparation subsystem,a sample collection subsystem, an optional collected sample pretreatmentsubsystem, a sample delivery subsystem, an analyte retention device(which includes the membrane described), an optional sample collectionand retention device flushing subsystem, a drying subsystem, an analysissubsystem and an optional data archiving subsystem.

The membrane contains minimal or no amount of the analyte of interest orminimal amounts or zero chemical bonds similar to the chemical bonds inthe analyte of interest, which bonds may interfere with the wavelengthdetection range or ranges of interest. If the membrane contains theanalyte or chemical bonds similar to the analyte, it must be such thatthey can be accounted for in the analysis of the tested membrane. Forthe purpose of determining hydrocarbon content in water, for example,the membrane contains minimal or zero hydrocarbon bonds which interferewith the wavelength detection range or ranges of interest. In thisparticular example, the membrane may be used to determine the type ofhydrocarbon molecule present, and thus can differentiate TPH from TOG,without any separate sample preparation.

It is to be understood that while an emphasis of the disclosure of thepresent invention is directed to the detection of hydrocarbons in water,it is to be understood that the features and attributes of the inventionmay be used to aid in the detection of analytes generally and in otherfluids including, but not limited to, air.

These and other features and advantages of the present invention willbecome apparent upon review of the following detailed description, theaccompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a simplified representation of the primary subsystems ofthe apparatus of the present invention.

FIG. 2 depicts a simplified representation of the analysis method of thepresent invention.

FIG. 3 is a cross sectional side view of a first embodiment of theanalyte retention device of the present invention.

FIG. 4 is a plan view of the membrane and seal of the retention deviceof the present invention.

FIG. 5 is a cross sectional side view of the membrane, seal and supportof the retention device.

FIG. 6 is a cross sectional side view of a first embodiment of theretention device connected to a flow expander.

FIG. 7 is a cross sectional side view of the retention device of FIG. 6with the membrane shown subjected to an IR beam.

FIG. 8 is a cross sectional view of a second embodiment of the retentiondevice that does not require any manipulation prior to drying, flushingor measurement.

FIG. 9 is a cross sectional side view of the retention device of FIG. 8with the membrane shown subjected to an IR beam.

FIG. 10 is a cross sectional view of a third embodiment of the retentiondevice in which the support is not a separate unit integrated into themolded device housing, but instead the molded housing itself performsthe function of the support.

FIG. 11 is a cross sectional side view of the retention device of FIG.10 with the membrane shown subjected to an IR beam.

FIG. 12 is a cross sectional side view of the retention device of FIG.6, showing a portion of the optional flow expander removed.

FIG. 13 is a cross sectional side view of the embodiment of theretention device of FIG. 12 with the membrane shown subjected to an IRbeam.

FIG. 14 is a cross sectional elevation view of a fourth embodiment ofthe retention device of the present invention.

FIG. 15 is a cross sectional side view of the retention device of FIG.14 with a portion of the housing removed.

FIG. 16 is a cross sectional side view of the fourth embodiment of FIG.15 with the membrane shown subjected to an IR beam.

FIG. 17 is a cross sectional side view of the retention device of thefirst embodiment in proximity to an interface conduit for fluid transferfrom a source.

FIG. 18 is a plan view of the drying subsystem including the retentiondevice removably retained therein.

FIG. 19 is a plan view of the manifold of the drying subsystem shown inFIG. 18.

FIG. 20 depicts FTIR spectra from the results of experiments using oneembodiment of the invention. Concentrations of hexadecane in water from0.1 ppm to 30 ppm were tested.

FIG. 21 depicts the FTIR spectrum from the results of an experimentusing one embodiment of the invention. A concentration of stearic acidin water at about 2.3 ppm was tested.

FIG. 22 depicts FTIR spectra from the results of experiments using oneembodiment of the invention to examine four samples of real waste water.

FIG. 23 is a table representing the results of experiments conducted onsix real-world fluid samples using the present invention in comparisonto a standardized solvent-based analysis of produced water from crudeoil production platforms in the Gulf of Mexico.

FIG. 24 shows an exploded view of a retention device constructed inaccordance with a fifth embodiment of the present invention.

FIG. 25 shows a retention device constructed in accordance with a sixthembodiment of the present invention, wherein the retention device ismounted in a bypass line.

DETAILED DESCRIPTIONS OF PREFERRED EMBODIMENTS OF THE INVENTION

In general, the present invention relates to the determination ofanalytes in fluids and, more particularly, to the determination ofhydrocarbons in water. Hydrocarbons in water are known to be harmful tothe environment and human health. ‘Water’ can indicate fresh water, seawater, municipal waste water, petroleum industry produced water (as usedherein, “produced water” means waste water produced, for example, incrude oil pumping or during industrial processing), bilge water fromships, and other waters. Each source of water has a limit to theconcentration of hydrocarbons that can be present before the water canbe discharged to the environment. Regulatory agencies worldwide enforcethese limits by requiring periodic testing at industrial sites andothers where hydrocarbons may be present in the water. The presentinvention seeks to provide an accurate, economical, rapid,environmentally-friendly solution to the problem of measuringhydrocarbons in water.

As illustrated in FIG. 1, an analysis apparatus 10 of the presentinvention includes a sampling device 12, an optional samplepre-treatment subsystem 14, a sample preparation subsystem 16, a samplecollection subsystem 18, an optional collected sample pretreatmentsubsystem 22, a sample delivery subsystem 24, an analyte retentiondevice 26, an optional sample collection and retention device flushingsystem 27, a drying subsystem 28, an analysis subsystem 30 and anoptional data archiving subsystem 32. Additionally, the fluid sample tobe analyzed may optionally be collected directly in the samplecollection subsystem 18 and processed through the subsequent stepsdescribed above.

The sampling device 12 is used to retrieve a fluid sample to be analyzedfor one or more analytes of interest. The sampling device 12 is selectedto conform to regulatory requirements for containers suitable to retaintherein a batch of a fluid to be analyzed. The sample device 12 shouldbe fabricated of an inert material, i.e., something that isnon-extractable and that yields no or minimal loss/degradation ofanalyte during storage and any travel. The sampling device 12 may beselected for suitability in an automated operation of a portion or allof the analysis apparatus 10. A glass container with sealable cap is asuitable sampling device, provided it includes a port sufficiently sizedto receive the fluid under analysis coming from a source of knowncharacteristics, such as a faucet, a pond or a conduit, for example. Aone-liter glass beaker with a Teflon®-lined cap has been found to besuitable as the sampling device.

The optional sample pre-treatment subsystem 14 is used to condition thesample, if deemed suitable, prior to transfer to the analyte retentiondevice 26. Such pretreatment may be necessary, for example, when asignificant period of time may pass between sampling and processing inorder to preserve the sample; or to condition the sample in preparationfor processing. It is selected as a tool or a method that is arranged toconform to standard and/or regulatory requirements, such aspre-treatment to acidify the fluid, for example. The optional samplepre-treatment may be conducted in the sampling device 12 or anothersuitable container having characteristics conforming to thecharacteristics of the sampling device 12. The optional samplepre-treatment subsystem 14 is selected to ensure that it does not effector impact the detection of the analyte in the fluid. The optional samplepre-treatment subsystem 14 may be selected for suitability in anautomated operation of a portion or all of the analysis apparatus 10.

As set forth above, the sample that has been collected may be acidified.In addition to acidification, the collected sample may be mixed with asurfactant to promote a uniform distribution of the analyte (e.g.hydrocarbons) in the sample. The surfactant is a fluorinated surfactanthaving a fluorinated alkyl chain with an anionic, cationic or nonionicheadgroup. Examples of fluorinated surfactants that may be used includeperfluorobutyl ethyl ether, perfluorobutyl methyl ether,tetrabutylammonium perfluorooctanoate, tetrapropylammoniumperfluorooctanoate and dibutyldipropylammonium perfluorooctanoate.

The sample preparation subsystem 16 includes one or more tools suitablefor preparing the gathered sample for analysis. The sample preparationsubsystem 16 is arranged to effectively agitate the sample to ensure ahomogeneous sample prior to transfer to the sample collection subsystem18. The sample preparation may be performed such as by manual shaking,automated shaking, using a laboratory mixer, magnetic stirring,ultrasonic mixing or a combination thereof. Heat may be useful to aidsample homogenization, either prior to or during the agitation step. Theaddition of metal oxide particulate in the size range 0.5 micron to 100micron may aid homogenization when added to the sample collectionsubsystem at the time of fluid sample collection or just prior toagitation. Such particulate should not be in sufficient concentration orof such composition so as to interfere with the analysis of the fluidsample for the analyte of interest. Shaking the sample horizontally hasbeen found to be particularly effective in agitating a sample comprisingone or more hydrocarbons and water. This shaking may be performed on thesampling device 12 (e.g. 1 liter bottle) containing the sample. Anexample of a commercially available horizontal shaker that may be usedis an Excella E1 platform shaker sold by New Brunswick Scientific Co.,Inc. Other suitable automated shakers include the Model 94605 shakersold by Central Pneumatic Paint Shaker of Camarillo, Ca. and theStirring Hotplate sold by Cole Parmer Thermo Scientific of Vernon Hills,Ill. An example of a suitable ultrasonic mixer, which breaks upparticles, is the IKA Ultra-TulTax T-18 Homogenizer made available byDaigger of Vernon Hills, Ill. The sample preparation subsystem 16selected may be operated based on suitable time and techniquecharacteristics that ensure homogenization of the sample. The samplepreparation subsystem 16 may be selected for suitability in an automatedoperation of a portion or all of the analysis system.

The sample collection subsystem 18 is used to remove a selectable volumeof the fluid under analysis from the sampling device 12, or optionallyused to directly retrieve the fluid sample to be analyzed, for transferto the analyte retention device 26. It is selected to have at least thefollowing characteristics. It must be able to effectively draw, house,and deliver sample under test. It could be traceable to a deliveryaccuracy standard, such as NIST and/or ISO manufacturing standards. Itshould effectively handle wide pressure range and positive pressures. Itis selected so that it does not introduce oil, grease, other any otheranalyte interferents. It is preferably disposable and/or retained insterile sealed containment, but need not be. It is a closed system so asto eliminate or minimize the possibility of introducing externalcontamination into the analysis process. It could have a standardizedcoupling interface, such as a standard connection, for example, a LUERinterface. The sample collection subsystem 18 is inert and made of amaterial that is non-extractable; that is, a material that will notleach into the fluid stream during the analysis method process.

The sample collection subsystem 18 is selected to enable smooth sampledrawing with a positive safety stop to prevent accidental spills. Itshould be accurate, with easy-to-read fine increments for sampletransfer with precision. The sample collection subsystem 18 ispreferably arranged to be capable of being adapted to the optionalsample collection and retention device flushing subsystem 27 to ‘flush’any remaining analyte through the system, including the retention device26, as desired. It is also preferably arranged for adaptation to theoptional sample pretreatment subsystem 22 in order to filter outpotential interferents and/or treat the sample to optimize analysis.Finally, the sample collection subsystem 18 may be selected forsuitability in an automated operation of a portion or all of theanalysis apparatus 10. The nonpyrogenic, nontoxic, sterile Norm-JectLUER Lock syringe available from Henke Sass Wolf of Tuttlingen, Germanyis a suitable embodiment of the sample collection subsystem 18.

The optional collected sample pretreatment subsystem 22 may be used tocondition the fluid just prior to transfer to the retention device 26,such as by filtering out any interferents that may adversely impact theanalysis method. It is selected to have at least the followingcharacteristics. It filters out any extraneous material that may havebeen introduced in the acquisition of the original sample batch orintroduced via any of the upstream subsystems. It is preferably arrangedto be compatible with at least the sample collection subsystem 18, thesample delivery subsystem 24, and the analyte retention device 26. It iscapable of filtering out chemical and/or physical interferent materials(e.g. particulate matter) without compromising analyte, data quality, orsystem accuracy. It is selected so as not to introduce interferents tothe fluid under analysis. It may retain a low volume of the fluidtreated so as to maximize the sample volume presented to the analyteretention device.

The optional sample pretreatment subsystem 22 is preferably disposableand/or retained in sterile seated containment, but need not be. It is aclosed system so as to eliminate or minimize the possibility ofintroducing external contamination into the analysis process. Finally,the sample pretreatment subsystem 22 may be selected for suitability inan automated operation of a portion or all of the analysis apparatus 10.The sample pretreatment subsystem 22 may be formed by a combination of aMillipore syringe filter, Millex-HV/PB filter unit, both available fromMillipore Corporation of Billerica, Mass., and a chemically-inert filtermaterial such as, but not limited to glass fibers, for example.

The sample delivery subsystem 24 is used to physically transfer preparedsample from collection/pretreatment to the analyte retention device 26.It is selected and arranged to include at least the followingcharacteristics. It is capable of providing optimal differentialpressure through the sample collection subsystem 18, the optional samplepretreatment subsystem 22, and the analyte retention device 26 withoutcompromising materials or results. It may either provide manual orautomated delivery of the sample. In the manual form, the sampledelivery subsystem 24 may simply be the piston of the syringe of thesample collection subsystem 18 actuated by hand, or it may be a modifiedadhesive gun. Manual delivery may or may not include a feedbackmechanism to characterize flow rate and pressure. In the automated form,the sample delivery subsystem 24 may be a syringe pump, such as theRemote Infuse/Withdraw PHD 22/2000 syringe pump made available byHarvard Apparatus of Holliston, Mass. Alternatively, it may be amodified power adhesive gun. The automated tool may or may not includefeedback control of pressure and/or flow rate—depending on applicationrequirements. The automated delivery embodiment is preferable in that itis more likely to provide accurate controlled delivery (e.g. totalvolume, flow rate profile and pressure profile).

The sample delivery subsystem 24 is preferably selected so that it doesnot introduce any contaminants or analyte interferents into the process.It may be adapted to provide sample agitation if necessary to assist inmoving particulate-laden samples through the system. For example, in theautomated form, it may include vibrational shaking, such as with anoff-balance motor, or acoustic pulsing, such as with a sonic energy pen.The sample delivery subsystem 24 may be selected for suitability in anautomated operation of a portion or all of the analysis apparatus 10.

The analyte retention device 26 described in greater detail herein, isconfigured to retain analytes (such as hydrocarbons) contained in thesample that has been collected. The retention device 26 includes atleast the following characteristics. It has no moving parts and requiresminimal or no manipulation to get the retained analytes there to theanalysis subsystem 30. It can handle wide differential pressure ranges(and thus a wide range of flow rates), including non-constant pressurefluid flows, e.g., constant flow rates, including positive pressuresexceeding 100 psi. More particularly, the retention device 26 isconstructed to operate under a positive pressure in a range from about 1to about 80 psi. It is capable of working with appropriate sample volumeranges based on the particular application of interest. The retentiondevice 26 is constructed so as to eliminate or minimize the possibilityof introducing external contamination into the analysis process. Theretention device 26 is fabricated of one or more inert andnon-extractable materials; that is, a material(s) that will not leachinto the fluid stream during the analysis process. The retention device26 may be selected for suitability in an automated operation of aportion or all of the analysis apparatus 10.

As illustrated in FIG. 2, an analysis method 100 of the presentinvention includes a plurality of steps, one or more of which may beoptional steps, for obtaining and preparing a sample of a fluid that mayinclude one or more analytes (such as hydrocarbons, for example) to bedetermined, and the steps associated with making that determination. Thefirst step of the method involves obtaining a sample of the fluid fromone or more selected sources. Next, the obtained sample may optionallybe pretreated as described herein, such as being acidified and/or havinga surfactant added thereto, for example. The sample, whether pre-treatedor not, is then prepared for collection. That step of preparation hasalso been described herein. At least a portion of the prepared sample isthen transferred to the sample collection subsystem for collection.Next, the collected sample may optionally be pretreated, also aspreviously described. The collected sample, whether pretreated, istransferred to the analyte retention device 26 in a manner that resultsin the fluid passing over or through a membrane to be described herein.For example, a syringe that is or that forms part of the samplecollection subsystem 18, may be connected to a connector of theretention device 26 and the sample may be pumped through the syringeusing a syringe pump that is or forms part of the sample deliverysubsystem 24 at a positive pressure of from about 1 psi to about 80 psiso as to be forced through the membrane to be described at a rate of 5ml/min. The syringe, the syringe pump and the retention device 26 areoriented such that the syringe is vertically disposed below theretention device 26 and the flow of sample is upwardly through thesyringe and the membrane. As a result of this orientation, air bubblesdo not interfere with the flow of sample through the membrane.

The sample collection subsystem 18 and the retention device 26 areoptionally flushed using the flushing subsystem 27, described herein.The retention device 26, whether flushed or not, is then dried in thedrying subsystem 28 and transferred to the analysis subsystem 30, whereit is then subjected to testing for the purpose of analyte detection,such as hydrocarbon detection. The information associated with theanalysis may then be used to perform calculations known to those ofordinary skill in the art. The apparatus 10 and the method 100 of thepresent invention are directed to an improved sample collectionarrangement so that the most effective sample is supplied to theanalysis subsystem 30. The resultant calculations performed, any sampleinformation and/or analysis information may optionally be reportedand/or archived in archiving subsystem 32.

As illustrated in FIGS. 3-5, the analyte retention device 26 generallyincludes a housing 40, a seal 42, a membrane 44, and a support 46, allto be described in greater detail herein with respect to specificembodiments depicted in a portion of the figures. In general, it isnoted that the housing 40 has a connector (such as a LUER connector) andmay be fabricated in an array of various designs optimized to meetspecific application (size, materials, flow rate, flow volumes,pressure) requirements. The seal 42 defines and establishes areproducible flow area. That is, it establishes a consistent sample flowarea, which flow area may be equivalent to an IR beam path crosssection, for example. The seal 42 seals the perimeter of the membrane 44and the support 46 so as not to allow analyte or interferent material toflow around/under the membrane 44 into the analysis field. Moregenerally, the seal 42 provides an air and liquid tight seal. Thematerial chosen for the seal 42 is selected to be physically andchemically robust enough to handle differential pressures across themembrane 44 and the support 46 without compromising materials oranalysis. It is also selected not to affect the IR processing of thesample. The seal 42 may be formed from portions of the housing 40, thesupport 46 and/or a separate deformable structure, such as a gasket.

In general, the membrane 44 of the analyte retention device 26 isselected for optimally capturing analytes of interest as describedherein. The support 46 is, effectively, a neutral density component andis configured to provide rigidity to the membrane 44. The support 46 isconfigured so as to not block fluid flow through or across the membrane44. It is selected to be amenable for IR spectrometry of the analyte ofinterest, and is capable of standing up to differential pressures acrossthe membrane 44 without compromising the integrity of the othercomponents of the retention device 26.

The support 46 functions as a structural support for the membrane 44.The membrane 44 is porous and effectively acts to distribute the fluidunder analysis to pass therethrough or thereover. Similarly, the support46 is configured to aid, or at least not to disrupt, the homogeneity ofthe fluid cross section passing through or over the membrane 44. Forexample, the support 46 may also be porous. Its porosity may be the sameas or different from the porosity of the membrane 44. That porosity ofthe support 46 may be selected as a function of the size of the area ofthe membrane 44 that is actually subject to the analysis. When theentire surface of the membrane 44 is subject to analysis (i.e., the beampath of IR spectroscopy substantially matches the area of the membrane44), the support 46 may have relatively large pores, as long as itprovides support for the membrane 44. When only a portion of the surfaceof the membrane 44 is subject to analysis (i.e., the beam path of IRspectroscopy is less than the area of the membrane 44), the support 46should have relatively smaller pores so as to aid in distributing thefluid uniformly through or across the membrane 44.

The support 46 may be a separate component of the retention device 26that fits within the housing 40. In that case, the membrane 44 and thesupport 46 may together be removed from the housing 40 and inserted inthe test fixture. Alternatively, the support 46 may be formed as apermanent integral part of the housing 40 and only the membrane 44 maybe removed from the housing 40 and inserted into the test fixture. Inanother embodiment of the invention, the entire housing 40, containingthe membrane 44 or the membrane 44 and support 46, may be inserted inthe test fixture. It is also to be noted that one or more components ofthe retention device 26, including the housing 40, the support 46, orboth, may be reusable.

In a first embodiment of the retention device 26 (further designatedwith the reference numeral “a”) represented in FIGS. 6 and 7, thehousing 40 (further designated with reference letter “a”) includesexternal threading 48 suitable for removable coupling of the housing 40a to another device, such as flow expander 50. The flow expander 50 maybe used to distribute collected sample across the surface of themembrane 44, such as when the sample delivery subsystem 24 includes asyringe 52 that would otherwise direct a relatively narrow flow streamto the membrane 44. In this first embodiment, the housing 40 a may beremoved from the expander 50 by unthreading or other means, and theentire retention device 26 a may be inserted into the analysis subsystem30 for analysis. FIG. 7 illustrates the complete retention device 26 awith an IR beam 54 of an IR spectrometer directed to the membrane 44.

In a second embodiment of the retention device 26 (further designatedwith the reference numeral “b”) represented in FIGS. 8 and 9, thehousing 40 (further designated with the reference letter “b”) is formedinto a shape that produces the equivalent effect of the flow expander 50of FIG. 6. Specifically, the housing 40 b includes a gradual taperedsection extending away from the location of the support 46 and themembrane 44. The end of the housing 40 b is sized to include internaldimensions that substantially match, but slightly exceed, the outerdimension of the terminus of the fluid directing means, such as the endof the syringe 52. In this second embodiment, the retention device 26 bmay be separated from the fluid directing means, and the entireretention device 26 b may be inserted into the analysis subsystem 30 foranalysis. FIG. 9 illustrates the complete retention device 26 b with theIR beam 54 of an IR spectrometer directed to the membrane 44.

In a third embodiment of the retention device 26 (further designatedwith reference letter “c”) represented in FIGS. 10 and 11, the housing40 (further designated with reference letter “c”) is formed into a shapethat produces the equivalent effect of the flow expander 50 of FIG. 6.Specifically, the housing 40 c includes a sharply tapered sectionextending away from the location of the support 46 and the membrane 44.The end of the housing 40 c is sized to include internal dimensions thatsubstantially match, but slightly exceed, the outer dimension of theterminus of the fluid directing means, such as the end of the syringe52. In this third embodiment, the retention device 26 c may be separatedfrom the fluid directing means, and the entire retention device 26 c maybe inserted into the analysis subsystem 30 for analysis. FIG. 11illustrates the complete retention device 26 c with the IR beam 54 of anIR spectrometer directed to the membrane 44. It is to be noted that thesupport 46 shown in FIGS. 10 and 11 is a porous embodiment thereof. Asearlier noted, the support 46 may or may not be porous.

FIGS. 12 and 13 illustrate the retention device 26 of FIGS. 6 and 7, inwhich a portion of the expander 50 may be cut and the remainder leftconnected to the retention device 26 for insertion in the analysissubsystem 30.

A fourth embodiment of the retention device 26 (further designated withreference letter “d”) of the present invention is illustrated in FIGS.14-16. In this fourth embodiment, housing 40 (further designated withreference letter “d”) forms part of the sample delivery subsystem 24,which may include a piston drive 56 to direct collected sample to themembrane 44 substantially across its entire cross sectional area. Inthis arrangement, no expander is required to create sample flowuniformity. The housing 40 d may be cut, as shown in FIG. 15, such thatonly a portion containing the membrane 44 forms part of the retentiondevice 26 d for transfer to the analysis subsystem 30. The IR beam 54 isthen directed to the membrane 44.

A fifth embodiment of the retention device 26 (further designated withreference letter “e”) is shown in FIG. 24. In this fifth embodiment,housing 40 (further designated with reference letter “e”) has atwo-piece construction and includes a flow expander 110 releasably andthreadably secured to a base 112. The flow expander 110 includes aconnector 114 (such a LUER connector) joined by a tapered section to acylindrical main section 116, which has internal threads and an outertextured surface. An annular interior ledge or shoulder 118 is formed atthe juncture of the tapered section and the main section 116. The base112 includes a first section 120 having external threads and a secondsection 124 having an outer textured surface. The second section 124 mayoptionally have internal threads. The flow expander 110 is secured tothe base 112 by threadably engaging the external threads of the firstsection 120 of the base 112 with the internal threads of the mainsection 116 of the flow expander 110.

In the fifth embodiment, the retention device 26 e includes a gasket 126composed of an elastomeric material, such as silicone. The membrane 44is positioned between the gasket 126 and the support 46. When the flowexpander 110 is secured to the base 112, the gasket 124 is pressedagainst the shoulder 118 of the flow expander 110, the support 46 ispressed against an annular end of the first section 120 of the base 112and the membrane 44 is pressed between the gasket 124 and the support46. In this manner, the membrane 44 is secured in the housing 40 e andthe gasket 126, the shoulder 118, the support 46 and the end of thefirst section 120 form the seal 42.

Another benefit of the retention device 26 e is that it permits ananalyte extraction method to be performed in a clean and facile manner.In accordance with this method, the retention device 26 e is moved to anupright position, wherein the connector 114 of the flow expander 110 isoriented downwardly and the second section 124 of the base 112 isoriented upwardly. A syringe (sample collection subsystem 18) isconnected to a connector 114 of the retention device 26 e and 10 ml ofthe sample is pumped through the syringe, such as by using a syringepump (sample delivery subsystem 24), at a positive pressure of fromabout 5 psi to about 30 psi so as to be forced through the membrane 44at a rate of 5 ml/min. The syringe, the syringe pump and the retentiondevice 26 e are oriented such that the syringe is vertically disposedbelow the retention device 26 e and the flow of sample is upwardlythrough the syringe and the membrane 44. The sample that passes throughthe membrane 44 collects in the base 112. Once the sample has beenpassed through the membrane 44, the retention device 26 e may be moved,while still in the upright position, to a disposal location, where theliquid (water) that has collected in the base 112 may be poured out ofthe base 112 and appropriately discarded.

The construction of the retention device 26 e also permits the membrane44 to be facilely removed from the housing 40 e after the sample hasbeen passed through the membrane 44. The removed membrane 44 may then beanalyzed in the analysis subsystem 30. Of course, the entire retentiondevice 26 e may be installed in the analysis subsystem 30 and themembrane 44 analyzed in situ. In this latter method, the beam of an FTIRspectrometer may be directed through the opening in the connector 114.

As illustrated in FIG. 17, the retention device 26 a including housing40 a with threading 48 may optionally be coupled to an interface conduit60 with valve 62. The conduit 60 may be joined to a process flow pipe 64within which a fluid of interest flows. In this arrangement, a sample ofthe fluid may be collected from the process flow pipe 64 withoutdisruption. In addition, samples may be collected when desired andwithout use of the various collection and transfer steps describedherein. A portion of the fluid within the process flow pipe 64 may beselectively directed to the membrane 44 of the retention device 26 byopening the valve 62. That is, the interface conduit 60 may beconfigured to divert a portion of the fluid toward the retention device26. The diversion may be achieved with a curved elbow as illustrated,but is not limited thereto. When a sufficient amount of the fluid haspassed through or over the membrane 44, the valve 62 may be closed. Theretention device 26 may then be disconnected from the interface conduit60 and treated and/or transferred to the analysis subsystem 30. Those ofskill in the art will recognize that other means for establishing adisconnectable interface to a structure where a fluid of interest islocated will provide the equivalent opportunity for sample collection onthe membrane 44. Further, the retention device 26 could be directlyconnected to the process flow pipe 64, with the retention device 26being detachably connectable to the process flow pipe 64. In thatarrangement, the flow of the fluid may or may not have to be haltedprior to removal of the retention device 26. Moreover, it is to beunderstood that the process flow pipe 64 is representative of a fluidsource and that the present invention is not limited to direct orindirect coupling of the retention device 26 to the fluid source.

A variation of the installation of FIG. 17 is shown in FIG. 25. In thisvariation, a sixth embodiment of the retention device 26 (furtherdesignated by the reference numeral f) is utilized. The retention device26 f has substantially the same construction as the retention device 26a, except both ends of the housing 40 (further designated with thereference numeral f) are threaded. In addition, the housing 40 f mayhave a more robust construction, e.g., the housing may be constructed ofmetal as opposed to plastic. The retention device 26 f is removablyconnected into a bypass line 130 that includes spaced-apart pipesections 132, 134 with threaded ends. Ends of the housing 40 f areremovably connected to the pipe sections 132, 134, respectively, byinternally threaded couplings 136, 138. Solenoid-actuated shut-offvalves 142, 144 are connected into the bypass line 130 on opposite sidesof the retention device 26 f. The shut-off valves 142, 144 may beremotely controlled by a microprocessor-based controller 146. A flowmeter 150 is also connected into the bypass line 130, downstream of theshut-off valve 142. The flow meter 150 is operable to measure the flowof sample in the bypass line 130 and transmit the measurement to thecontroller 146.

The controller 146 has memory and a processor operable to execute asample program stored in the memory. When executed, the sample programopens the shut-off valves 142, 144, thereby causing sample from theprocess flow pipe 64 to flow through the bypass line 130 and, thus,through the retention device 26 f. After a predetermined amount ofsample (as measured by the flow meter 150) has flowed through the bypassline 130 or after a predetermined amount of time, the sample programcloses the shut-off valves 142, 144. The sample program may then alsonotify remotely located service personnel that the sample collection iscompleted. In response, the service personnel may remove the retentiondevice 26 f from the bypass line 130 by unthreading the couplings 136,138. The removed retention device 26 f may then be treated (dried etc.)and then transferred to the analysis subsystem 30 where the amount ofhydrocarbons in the sample are measured. Since the amount of sampleflowing through the retention device 26 f is measured by the flow meter150 and, thus, is known, the percentage of hydrocarbon in the samplethat flowed through the bypass line 130 can be determined.

Returning to FIG. 1, the optional sample collection and retention deviceflushing subsystem 27 may be used to ensure that all sample fluid passesthrough the retention device 26 so that only the analyte remainsthereon. It is selected to have at least the following characteristics.It is preferably arranged for adaptation to the sample collectionsubsystem 18 and the optional sample pretreatment subsystem 22. It iscapable of filling the sample collection subsystem 18 with anappropriate fluid (e.g. clean water) to: 1) rinse and flush potentiallyremaining analyte through the retention device 26; and 2) help optimizethe analytical performance of the overall system. The sample collectionand retention device flushing subsystem 27 is easily adaptable to samplecollection and optional sample pretreatment subsystems via common, inertconnections (e.g. LUER connections) that provide unidirectional flow ofdesired fluid through the retention device 26 during a flushing step, ifthat optional step is conducted, after analyte sample delivery.

This optional sample collection and retention device flushing subsystem27 is preferably disposable and/or retained in sterile sealedcontainment, but need not be. It is a closed system so as to eliminateor minimize the possibility of introducing external contamination intothe analysis process. The sample collection and retention deviceflushing subsystem 27 is fabricated of one or more inert andnon-extractable materials; that is, a material(s) that will not leachinto the fluid stream during the analysis process. Finally, the samplecollection and retention device flushing subsystem 27 may be selectedfor suitability in an automated operation of a portion or all of theanalysis apparatus 10. The three-way valve part no. DCV 115 availablefrom Value Plastics, Inc. of Fort Collins, Colo., connected to a sourceof appropriate flushing fluid is a suitable embodiment of the optionalsample collection and retention device flushing subsystem 27.

With reference to FIGS. 1, 18 and 19, the drying subsystem 28 is used toremove non-analyte fluid (e.g. water) from the retention device 26 priorto conducting the analyte analysis steps of the method of the presentinvention. The drying subsystem 28 includes housing 60, manifold 62 andinterface 64. The housing 60 includes a cavity within which theretention device 26 may be removably affixed. Specifically, the housing60 includes an inlet 66 that may be configured with a reversiblyconnector to join to the housing 40 of the retention device 26. Forexample, each may be threaded. The inlet 66 is further configured forreversible connection to the interface 64 at first interface end 68. Theinterface is arranged to establish a conduit through which a dryingmedium, such as air, for example, passes into the housing 60 through theinlet 66. Second interface end 70 of the interface 64 is arranged forreversible connection to the manifold 62. The manifold is arranged witha plurality of drying tubes 72, wherein one or more of the drying tubes72 may include a valve 74 to enable the user to regulate drying mediumflow to the membrane 44 of the retention device 26. For example, theuser may wish to open one or more valves partially or completely togenerate lateral drying, i.e., drying of the top surface of the membrane44. Alternatively, the user may wish to close all valves and leave onedrying tube 72 open, such as the center one shown in FIG. 17, for thepurpose of forcing the drying medium through the membrane 44.Alternatively, in conjunction with the pressurized drying media directedthrough the membrane 44 described above, it may be suitable toadditionally direct a drying media, at the analyte retention device 26output, specifically to impinge on the membrane support. Other optionsfor drying orientation, as well as time frames, drying media, and thelike will be recognized by those of skill in the art. It is to beunderstood that the components of the drying subsystem 28 may befabricated of selectable materials including, but not limited to,nonmetallic materials, provided the materials selected do not adverselyimpact the intended functionality of the system 10.

It is to be noted that the connection of the drying subsystem 28 to theanalyte retention device 26 plays an important role in removingnon-analyte fluid/vapors from the membrane 44 and within the housing 40in preparation for analysis. The drying subsystem 26 is configured tohave at least the following characteristics. It is selected to optimizethe effect of the drying subsystem 28 to efficiently and effectively drythe analyte retention device 26 prior to analysis without removingretained analyte or introducing interferents or contaminations thatwould otherwise compromise the analysis process. There may be manual,semi-automated, or automated versions of the drying subsystem 26.

The drying subsystem 26 is designed by encapsulating an input sourcedrying air source internal to a secondary flow dynamics andpressure-controlling assembly. As noted, the manifold 62 is configuredto provide the capability to dry the membrane 44 by allowing lateral(across the top of the membrane 44) and/or vertical (through themembrane 44) flow paths and exhaust. The distribution of the lateral andvertical flow amounts can be controlled via the valves 74. The manifold62 may incorporate automation (e.g. sensors and electronic valves) forfeedback and control of the lateral and vertical analyte retentiondevice 26 drying air profile (e.g. time, rate, pressure,lateral/vertical flow distribution).

The drying subsystem 28 may be selected for suitability in an automatedoperation of a portion or all of the analysis system. Examples ofsuitable embodiments of the drying subsystem 28 include, but are notlimited to, The Norm-Ject syringe from Henke Sass Wolf, any commerciallyavailable air pump, such as the Air Pump 7500 made available by PetcoAnimal Supplies, Inc. of San Diego, Calif., an air compressor, such asthe TC-20 Compressor made available by TCP Global of San Diego, Calif.More generally, other means for drying include, but are not limited to,mechanically compressed ambient air, mechanically compressed, dried, andfiltered ambient air, and sources of pressurized process gases (e.g.air, nitrogen). As noted, a pressure feedback tool may be employed toobserve and regulate the air flow rate of the drying subsystem 28. Inaddition, a Drierite™ drying tube, such as one available from W. A.Hamilton Co. Ltd. of Xenia, Ohio, may be used to aid in drying theretention device 26.

With regard to hydrocarbons-in-water analysis it is important that wateris mostly removed from the membrane 44. Water absorbs strongly in theinfrared, with a peak centered approximately at 3400 cm⁻¹. When too muchwater is present on the membrane 44, the peak due to water extends intothe region where peaks due to hydrocarbons appear, which leads toinaccurate analysis. In addition, the peak due to water can potentiallyinfluence the placement of baseline points, which also leads toinaccurate analysis. The proper amount of drying of the membrane 44 canbe determined from an absorption spectrum when one or more hydrocarbonpeak(s) between about 2850 cm⁻¹ and about 3000 cm⁻¹ can be distinguishedfrom the water peak at about 3400 cm⁻¹. Such detection of separatehydrocarbon peaks can be performed visually by an operator viewing adisplay of the spectrum generated by the analysis subsystem 30 orautomatically by an analysis program executed by the analysis subsystem30.

The analysis subsystem 30 is used to conduct the evaluation of thecharacteristics of any analytes retained on the analyte retention device26 after the drying process. The retention device 26 or a portionthereof is either deployed in a test fixture frame or other form ofsupport of the analysis subsystem 30. The analysis subsystem 30 includesat least the characteristics of IR technology (or equivalent). Thattechnology includes radiometric (one small window over the IR spectrum),semi-radiometric (multiple small windows over different regions of theIR spectrum), or full spectrographic depending on applicationrequirements. The analysis subsystem 30 is capable of signal processingfor baseline correction, integration, peak height determination andspectral analysis (chemimetrics and/or related statistical processing).It preferably at least includes information storage capacity, one ormore libraries of known analyte IR characteristics, a user interface,wired or wireless communication capability, and is capable of receivingand supporting at least the membrane 44 with a scan field similar orless in cross sectional dimensions to the cross sectional dimensions ofthe membrane 44. It must provide an output of information of sufficientdetail to enable one of ordinary skill in the art to be able to make adetermination as to the analyte content of the fluid of the gatheredsample. The analysis subsystem 30 may be automated and may further beselected for suitability in an automated operation of a portion or allof the complete analysis apparatus 10. Suitable embodiments of theanalysis subsystem 30 include, but are not limited to, the MB 3000 FTIRand Horizon software made available by ABB Bomen of Quebec, Canada andthe Nicolet iZ10 and the Grams/AI Analysis software made available byThermoFisher Scientific of Waltham, Mass.

The optional archiving subsystem 32 may be used to store raw andprocessed information from the analysis process. Its characteristicsinclude, but are not limited to including, sufficient capacity to storeelectronically any information of interest regarding the sample,analysis and the process. It effectively stores raw and processedinformation for potential re-analysis. If located in an environment thatmay be adverse, it is preferably retained in a secure, environmentallyconditioned, sealed air- and liquid-tight container. It should be wireor wirelessly couplable to one or more other subsystems of the analysisapparatus 10 in a manner that ensures there is no compromise of theintegrity of the apparatus 10 and its sampled result for a determinedamount of time (dependent on application). As with the other subsystems,the optional archiving subsystem 32 may be selected for suitability inan automated operation of a portion or all of the complete analysisapparatus 10.

A specific description of the components of the analyte retention device26 and analysis subsystem 30 follows.

The membrane 44 includes a base material with a surface treatment. Thebase material is porous and is made of a fluorine-containing polymer,such as polytetrafluoroethylene (PTFE), a fluorinated ethylene-propylenecopolymer, an ethylene-tetrafluoroethylene copolymer or aperfluoroalkoxy polymer. PTFE has been found to be particularlysuitable. The base material has a thickness between about 25 μm and 150μm, more particularly between about 45 μm and 85 μm, still moreparticularly about 65 μm. The base material has a nominal pore size in arange from about 0.2 μm to about 0.6 μm, more particularly from about0.4 μm to about 0.5 μm, still more particularly about 0.45 μm.

The surface treatment renders the membrane 44 hydrophilic, whichpromotes uniform distribution of the sample to be analyzed across thesurface area of the membrane 44 and facilitates fluid flow through themembrane 44. The surface treatment may be a monolayer or multilayercoating of selectable thickness. The coating may be poly(ethyleneoxide). The coating may alternatively be a perfluorocarbon copolymer. Anexample of such a perfluorocarbon copolymer is a co-polymer of at leasttwo monomers with one monomer being selected from a group offluorine-containing monomers such as vinyl fluoride,hexafluoropropylene, vinylidene fluoride, trifluoroethylene,chlorotrifluoroethylene, perfluoro(alkylvinyl ether),tetrafluoroethylene and mixtures thereof. The second monomer is selectedfrom a group of fluorine-containing monomers containing functionalgroups which can be or which can be converted to (SO₂F), (SO₃M), (SO₃R),(SO₂NR₂), (COF), (CO₂M), (CO₂R) or (CONR₂) groups, where M is hydrogen(H), an alkali metal, an alkaline earth metal, or NR₄ and each Rseparately is H, an alkyl group or an aryl group, such as CH₃, C₂H₅ orC₆H₅, and may, optionally, contain other functional groups such ashydroxyl, amine, ether or carbonyl groups or the like to formsubstituted alkyl or substituted aryl groups.

The hydrophilic coating may be applied to the base material of themembrane 44 using a solution comprising a solvent and theperfluorocarbon copolymer. The solvent may be an alcoholic solvent, suchas methanol, ethanol, n-propanol or isopropanol, which may mixed withwater. The solution may be applied to the base material by immersing thebase material in the solution, or by passing the solution through themembrane under a pressure differential.

Depending on the particular embodiment in which it is used, the membranesupport 46 may be nonporous or porous. When porous, the membrane support46 may have a nominal pore size in a range from about 100 μm to about 3mm, more particularly, in a range from about 100 μm to about 1 mm, stillmore particularly in a range from about 200 μm to about 300 μm, stillmore particularly about 250 μm. The support 46 may be made of plastic,metal or ceramic. Suitable metals include aluminum, platinum, andstainless steel and suitable plastics include poly(tetrafluoroethylene),polyethylene, polypropylene and polycarbonate. A stainless steel screenhas been found particularly suitable for use as the support 48.

The housing 40 is constructed from a material containing insignificantamounts of extractable organic material that may interfere with thedetermination of the amount of hydrocarbon present. The housing may beplastic, metal or ceramic. Suitable metals include stainless steel andaluminum. Suitable plastics include high density polyethylene (HDPE),low density polyethylene (LDPE), polypropylene andpolytetrafluoroethylene (PTFE), any of which may be surface treated witha coating suitable to improve, for instance, IR-amenability and/orreduce extractable content.

The configuration of the housing 40 can vary, as described in detailabove. In the configurations described above, the housing 40 isconfigured to provide for fluid flow through the membrane 44. It shouldbe appreciated, however, that the housing 40 may alternately beconfigured to provide for fluid flow across the surface of the membrane44. Furthermore, the housing 40 may be configured to be reusable, i.e.after directing the sample through or across the membrane 44, thehousing 40 can be opened, the membrane 44 or membrane 44 and support 46are removed, and the housing 40 is cleaned for re-use. The housing 40 isre-used by placing a membrane 44 or membrane 44 with support 46 into thehousing 40 and closing the housing 40, for example, by connectingthreaded pieces together.

The retention device 26 may also include in certain embodiments, a fluidpump such as, but not limited to, a peristaltic pump.

The analysis subsystem 30 includes: 1) in certain embodiments,dispersive spectroscopic devices; 2) in certain embodiments, FourierTransform spectroscopic devices; 3) in certain embodiments, AttenuatedTotal Reflectance spectroscopic devices; 4) in certain embodiments,dispersive radiometric devices; 5) in certain embodiments, AttenuatedTotal Reflectance radiometric devices. The embodiments of the analysissubsystem 30 listed can work by: 1) in certain embodiments, examiningthe absorbance in the infrared region of the electromagnetic spectrum;2) in certain embodiments, examining the absorbance in the near-infraredregion of the electromagnetic spectrum; 3) in certain embodiments,examining the absorbance in the ultraviolet region of theelectromagnetic spectrum; and 4) in certain embodiments, examining theRaman shift spectrum.

With regard to hydrocarbons-in-water analysis, the determination of thetype(s) of hydrocarbon(s) in the water can be determined from patternrecognition of the absorption bands in the spectrum. The bands aremeasured in various ways, namely height, area, curve fitting, baselinecorrections etc. Examples of how pattern recognition can be used todetermine the type of hydrocarbon(s) present include noting the presenceof the H—C═C band at 3006 cm⁻¹ and the C═O band at 1745 cm⁻¹, whichindicates components of vegetable oils, namely unsaturated oils andfatty acids. Also, diesel oil typically has a maximum absorption atabout 2927 cm⁻¹.

EXAMPLE

The invention now being generally described, it will be more readilyunderstood by reference to the following examples, which are includedmerely for purposes of illustration of certain aspects and embodimentsof the present invention, and are not intended to limit the invention.

Example 1

A PTFE membrane of thickness 50 .mu.m, nominal pore size 0.45 .mu.m, anddiameter 15 mm was placed over a metal support disk of 0.25 mm pores and12.7 mm diameter. The excess membrane material was wrapped around to theback of the metal support disk. PTFE washers of 7.1 mm inner diameter,12.7 mm outer diameter, and 0.75 mm thickness were placed on both sidesof the membrane and disk (See FIGS. 4 and 5). Approximately 30 psi. offorce is applied by hand to press the washers, membrane and disktogether; this is henceforth referred to as the supported membrane unit.The supported membrane unit was placed in a 13 mm infrared window holder(Bruker optics). Transmission Fourier Transform infrared (FTIR)spectroscopy was performed on an ABB FTLA 2000 with a liquid nitrogencooled mercury-cadmium telluride detector interfaced with a computer. Abackground spectrum was taken as the average of 50 scans. The supportedmembrane unit was then placed into a stainless steel filter holder fromAdvantec (P/N 30100) and tightened by hand to provide water tight sealaround the membrane.

Hydrocarbon-in-water test dispersions of concentration 0.1-30 ppm werecreated by first dissolving hexadecane in methanol and stirring forabout 20 min. Hexadecane was used here as a simulant for Oil. A certainamount of the methanol-hexadecane solution was then dispersed into thecenter of one liter of deionized water as it was being stirred at about300 rpm by a magnetic stir bar and stir plate. Thiswater-methanol-hexadecane dispersion was then allowed to stir for about20 minutes to ensure even distribution of hexadecane in water. As allconcentrations of hexadecane tested were well above the solubility limitof about 3 ppb in water, the solution existed as a two-liquid-phasesystem of hexadecane droplets dispersed in deionized water; the size ofthe droplets was not known.

After the set stir time, about 12 ml of the hexadecane-water dispersionwere drawn by hand into a low-extractable plastic syringe. The filterholder containing the supported membrane unit was then attached byLUER-lock to the syringe. The syringe was then placed on a syringe pumpset to pump 10 ml in 3 min. When the sample finished flowing, the filterholder was removed from the syringe, the syringe filled with air, thefilter holder re-attached to the syringe, and about 10 ml of air forcedthrough the membrane to dry it. This process was repeated two more timesto dry the membrane as a large amount of water present on the membranewould interfere with the infrared measurement. The filter holder wasthen removed from the syringe and opened. The supported membrane unitwas removed from the filter holder and again placed into the 13 mminfrared window holder. An FTIR spectrum was taken using thepreviously-obtained background spectrum, again averaging 50 scans. Fiveexperiments were performed at hexadecane concentrations of 0.1 ppm and 1ppm; two experiments were performed at hexadecane concentrations of 20ppm and 30 ppm.

The results of this experimentation are shown in FIG. 20, which shows arepresentative spectrum obtained by testing each of the fourconcentrations of hexadecane in water. At the high end of 30 ppmhexadecane, the absorbance peaks an easily quantifiable level of about0.7 absorbance. At the low end of 0.1 ppm hexadecane the peak absorbanceis about 0.0045, a level still significantly above the generallyaccepted minimum signal/noise ratio of 0.001 required forquantification. The peak absorbance can be controlled by syringingdifferent amounts of water and/or using a different membrane area. Forinstance, the results indicate a concentration of 300 ppm could betested and still in the quantifiable range by syringing about 1 ml or byexpanding the effective membrane area by about 10 times. At the low end,the results indicate a concentration of 10 ppb could be tested andquantifiable by syringing about 100 ml or by reducing the effectivemembrane area by about 10 times.

Example 2

The second example was similar to the first example. A supportedmembrane unit was made from the same materials, a background spectrumtaken, and the same filter holder used in the same way. The onlydifference was that a 2.3 ppm solution of stearic acid in water wastested. Stearic acid was dissolved in methanol and stirred for 20 min. Acertain amount of this solution was then added to 1 liter of deionizedwater and stirred for 20 min to create an even distribution of stearicacid in water. Stearic acid was used as a simulant for Grease. Grease isincluded in the TOG definition but not TPH.

The test was performed in the same way as in Example 1. Simply, 10 ml ofthe stearic acid dispersion in water was syringed through the supportedmembrane unit and dried in the same manner. However, a small amount ofwater remained. FIG. 21 shows the results of the test. Stearic acidstrongly absorbs at about 1700 cm.sup.−1, the carboxyl absorbanceregion, and in the hydrocarbon absorbance region of 2800-3000 cm.sup.−1.The spectrum shows that Grease can be measured so the invention can beused to determine TOG. However, Grease is an interferent for determiningTPH due to the overlapping absorbance in the region 2800-3000 cm.sup.−1.To address the problem, the absorbance at about 1700 cm.sup.−1 may beused to determine the amount of Grease present and subtract it from TOGto determine TPH.

Example 3

The third example is generally similar to the first two in that asupported membrane unit was made from the same materials and abackground spectrum taken. However, in this example, six differentsamples of six different fluids from real-world sources were run throughthe analysis system of the present invention, three times for each. Inaddition, a standard solvent-based EPA 1664 analysis was performed onthe same fluid samples to determine the relationship between the resultsobtained using the present invention and the current standard foroil-in-water detection. FIG. 22 shows the spectra resulting from testresults for four of the samples (excluding the samples from the Gulf ofMexico). Further, as can be seen from the table of FIG. 23, whichidentifies the sources of the six samples, the averaged results obtainedusing the present invention closely matched the results using theconventional solvent-based test method, wherein the conventionalsolvent-based method is identified as the 1664 Result.

Other variations of the above examples can be implemented. One examplevariation is that the described method may include additional steps.Further, the order of the steps is not limited to the order illustratedin FIG. 2, as the steps may be performed in other orders, and one ormore steps may be performed in series or in parallel to one or moreother steps, or parts thereof.

Additionally, certain of the analysis and determination steps of themethod and various examples of the analysis performed on the samplescollected on the membrane 44 of the retention device 26 and variationsof these steps, individually or in combination, may be implemented as acomputer program product tangibly as computer-readable signals on acomputer-readable medium, for example, a non-volatile recording medium,an integrated circuit memory element, or a combination thereof. Suchcomputer program product may include computer-readable signals tangiblyembodied on the computer-readable medium, where such signals defineinstructions, for example, as part of one or more programs that, as aresult of being executed by a computer, instruct the computer to performone or more processes or acts described herein, and/or various examples,variations and combinations thereof. Such instructions may be written inany of a plurality of programming languages, for example, Java, VisualBasic, C, or C++, Fortran, Pascal, Eiffel, Basic, COBOL, and the like,or any of a variety of combinations thereof The computer-readable mediumon which such instructions are stored may reside on one or more of thecomponents of a computing system well known to those of ordinary skillin the art.

A number of examples to help illustrate the invention have beendescribed. Nevertheless, it will be understood that variousmodifications may be made without departing from the spirit and scope ofthe invention. Accordingly, other embodiments are within the scope ofthe claims appended hereto.

1. A method of detecting one or more analytes in a fluid, the methodcomprising: providing a membrane formed of one or more materialsselected to produce a detectable change thereof as a result of makingcontact with the one or more analytes, the one or more materials beingselected to exclude any component in sufficient amount to interfere withthe detection of the one or more analytes; contacting the membrane withthe fluid; and analyzing the detectable change in the membrane.
 2. Themethod of claim 1 wherein the membrane is porous.
 3. The method of claim2, wherein the step of contacting the membrane comprises passing thefluid through the membrane.
 4. The method of claim 1, wherein the stepof contacting the membrane comprises passing the fluid over themembrane.
 5. The method of claim 1, further comprising the step ofhomogenizing the fluid before contacting the membrane with the fluid. 6.The method of claim 5, wherein the shaking of the fluid is performedhorizontally.
 7. The method of claim 1, wherein the step of analyzingthe detectable change is performed with an infrared spectrometer.